1. Technical Field
This invention relates to a linear motor driving an elevator, and more particularly to maintaining an air gap between primary and secondary portions thereof.
2. Background Art
A typical elevator system comprises an elevator car and a counter weight each suspended on opposite ends of a hoist rope disposed in an elevator hoistway. The elevator system also includes a linear motor generating a thrust force that facilitates movement of a counter weight. As the counter weight is alternatingly moved up and down by the linear motor the elevator car moves correspondingly thereto.
Linear motors include a rotor, frequently referred to as a secondary, and a stator, referred to as a primary. The primary or stator is typically attached to the counter weight and is engaged in linear motion, whereas the secondary or rotor is stationary and is fixedly attached to an inner wall of the hoistway.
To insure proper operation of the motor, a specified air gap must be maintained between the primary and secondary portions of the motor. The two portions of the motor are pulled together by attraction forces that exceed the thrust force of the motor. If the primary and secondary portions come in contact with each other, a short circuit may be caused. Furthermore, a small constant air gap increases efficiency as well. Thus, maintaining a constant air gap is of utmost importance. Older versions of the linear motors employ guide rails on which the primary motor was suspended, wherein these guide rails get deformed with time due to the attraction forces between the primary and secondary portions of the linear motor.
U.K. Pat. No. 2,237,555A disclosed a device for maintaining the air gap, which includes a single roller assembly and is attached to the moving primary motor. The air gap is maintained through the adjustment of two adjusting rods. However, there is still a need for more precise adjustment of the air gap and for an easier means of adjusting the air gap.